Tandem electrode welder and method of welding with two electrodes

Abstract

An electric arc welding apparatus comprising at least a first consumable electrode and a second consumable electrode movable in unison along a welding path between the edges of two adjacent, mutually grounded plates, a first power supply for passing a first welding current at a first low frequency between the first electrode and the two plates, a second power supply for passing a second welding current at a second low frequency between the second electrode and the two plates, where each of the power supplies includes a three phase voltage input operated at line frequency, a rectifier to convert the input voltage to a DC voltage link and a high frequency switching type inverter converting the DC voltage link to a high frequency AC current, an output rectifier circuit to provide a positive voltage terminal and a negative voltage terminal, and an output switching network operated at a given low frequency for directing a pulsating welding current at the given low frequency from the two terminals across one of the electrodes and the plates, and a circuit for independently adjusting the given low frequency so the value of the first low frequency of the first power supply is different from the second low frequency of the second power supply.

Having thus defined the invention, the following is claimed:  
     
       1. A method of electric arc welding the joint between two plates, said method comprising: 
       (a) moving at first and second consumable electrodes substantially in unison along said joint;  
       (b) at least periodically passing a first pulsating welding current between said first electrode and said plates with a first low frequency;  
       (c) at least periodically passing a second pulsating welding current between said second electrode and said plates with a second low frequency; and,  
       (d) at least partially controlling at least one of said low frequencies such that said first low frequency deviates from said second low frequency at least once as said at least first and second consumable electrodes are moved along said joint.  
     
     
       2. The method as defined in  claim 1 , wherein at least one of said low frequencies is at first partially varied as a function of time. 
     
     
       3. The method as defined in  claim 2 , wherein both of said low frequencies are at least partially varied as a function of time. 
     
     
       4. The method as defined in  claim 3 , wherein at least one of said pulsating currents is an AC current. 
     
     
       5. The method as defined in  claim 3 , wherein at least one of said pulsating currents is a DC current. 
     
     
       6. The method as defined in  claim 2 , wherein at least one of said pulsating currents is an AC current. 
     
     
       7. The method as defined in  claim 2 , wherein at least one of said pulsating currents is a DC current. 
     
     
       8. The method as defined in  claim 2 , wherein at least one of said welding currents is created by a high frequency switch inverter driven by a three phase line voltage. 
     
     
       9. The method as defined in  claim 8 , wherein said first and second welding currents are independently created from the same three phase power supply. 
     
     
       10. The method as defined in  claim 9  wherein at least one power supply that supplies at least one of said welding currents includes an inverter to convert AC voltage to a DC current source having a maximum current of at least about 200 amperes. 
     
     
       11. The method as defined in  claim 2 , wherein at least one of said welding currents is at least partially generated by at least one power supply having an output switching network at least partially operated at a given low frequency to direct a pulsating welding current at said given low frequency. 
     
     
       12. The method as defined in  claim 11 , wherein at least one power supply that supplies at least one of said welding currents includes a circuit to at least partially independently adjust said given low frequency so the value of said first low frequency is at least partially different from said second low frequency. 
     
     
       13. The method as defined in  claim 12 , wherein at least one of said low frequencies is less than about 300 Hz. 
     
     
       14. The method as defined in  claim 2 , wherein said first and second low frequencies are at least partially generated by the same power source. 
     
     
       15. The method as defined in  claim 2 , wherein at least one power supply that supplies at least one of said welding currents includes a pulse width modulator to control the voltage between said terminals as a function of time to adjust the welding current. 
     
     
       16. The method as defined in  claim 1 , wherein at least one of said pulsating currents is an AC current. 
     
     
       17. The method as defined in  claim 1 , wherein at least one of said pulsating currents is a DC current. 
     
     
       18. The method as defined in  claim 1 , wherein at least one of said welding currents is created by a high frequency switch inverter driven by a three phase line voltage. 
     
     
       19. The method as defined in  claim 18 , wherein said high frequency is at least about 20 kHz. 
     
     
       20. The method as defined in  claim 18 , wherein said first and second welding currents are independently created from the same three phase power supply. 
     
     
       21. The method as defined in  claim 18 , wherein at least one power supply that supplies at least one of said welding currents includes an inverter to convert AC voltage to a DC current source having a maximum current of at least about 200 amperes. 
     
     
       22. The method as defined in  claim 21 , wherein said AC voltage is three phase line voltage with a frequency of up to about 60 Hz. 
     
     
       23. The method as defined in  claim 1 , wherein at least one of said welding currents is at least partially generated by at least one power supply having an output switching network at least partially operated at a given low frequency to direct a pulsating welding current at said given low frequency. 
     
     
       24. The method as defined in  claim 23 , wherein at least one power supply that supplies at least one of said welding currents includes a circuit to at least partially independently adjust said given low frequency so the value of said first low frequency is at least partially different from said second low frequency. 
     
     
       25. The method as defined in wherein at least one power supply that supplies at least one of said welding currents includes a circuit to at least partially independently adjust said given low frequency so the value of said first low frequency is at least partially different from said second low frequency. 
     
     
       26. The method as defined in  claim 1 , wherein at least one of said low frequencies is less than about 300 Hz. 
     
     
       27. The method as defined in  claim 1 , wherein said consumable electrodes are advance welding wires. 
     
     
       28. The method as defined in  claim 1 , wherein said first and second low frequencies are at least partially generated by the same power source. 
     
     
       29. The method as defined in  claim 1 , wherein at least one power supply that supplies at least one of said welding currents includes a pulse width modulator to control the voltage between said terminals as a function of time to adjust the welding current. 
     
     
       30. The method as defined in  claim 1 , including a master controller to create a synchronizing signal directed to at least one power supply and having a succession of synchronizing commands and means for forcing said at least one power supply to start its low frequency current upon receipt of a synchronizing command. 
     
     
       31. The method as defined in  claim 30 , including a delay circuit to delay the receipt of said synchronizing command for said at least one of power supply for a selected time to phase shift said first and second welding currents. 
     
     
       32. The method as defined in  claim 30 , including means for creating at least one of said low frequencies upon receipt of said synchronizing command. 
     
     
       33. The method as defined in  claim 1 , including at least one said power supply that supplies at least one welding current having an output switching network to direct a welding current from terminals across one of said electrodes and said plates, and a circuit to independently adjust said output switching network so the value of a first welding current is at least partially different from a second welding current, said output switching network including a first switch to create positive current across one of said electrodes and said plate and a second switch to create a negative current across one of said electrodes and said plate and a circuit to operate said first and second switches to control said welding current. 
     
     
       34. The method as defined in  claim 33 , wherein said circuit includes a switch selector to maintain one of said switches closed and the other of said switches opened. 
     
     
       35. The method as defined in  claim 33 , wherein said circuit includes a switch selector to open and close said switches at a rate to create an AC welding current having a selected frequency of up to about 300 Hz.